1. Field of the Invention
This invention relates to the hydraulic conductivities of liquids through permeable materials and particularly relates to the conductivity of water through earth. It also relates to testing such conductivity from the surface of the earth to great depths beneath the surface and above the water table while preventing contamination by falling soil and debris. It more particularly relates to instruments that establish a static head of water within a borehole and maintain the water at this predetermined level by use of a float and valve system. It specifically relates to a float and valve system that provides a mechanical advantage ratio enabling use at such great depths.
2. Review of the Prior Art
It is often important to estimate the hydraulic conductivities of earthen materials in order to safely and economically develop lands for urban and agricultural uses. Hydraulic conductivity values are important considerations in design and construction of building and roadway foundations, on site sewage wastewater treatment systems, and storm water infiltration facilities. These values are important for artificial treatment of wetlands, and for estimating the rate of transport of liquid contaminants from waste disposal sites and leaking storage tanks. Hydraulic conductivity values are additionally important in design of irrigation systems and drainage of agricultural lands.
Soil hydraulic conductivity can be used to describe the ability of earthen materials to transmit water. Darcy""s Law describes the relationship of the volume of water, moving through a cross sectional area of soil (commonly known as flux) along the hydraulic gradient of the water flow path, to the hydraulic conductivity. Under saturated conditions, such as below a water table, hydraulic conductivity is referred to as saturated hydraulic conductivity. Even though Darcy""s law was originally developed to describe saturated flow, the principles of the law can be applied to water movement in partially saturated soils above the water table.
The determination of hydraulic conductivity under field conditions can be complicated because of the natural variation of soil properties and the specific need for which the test is being conducted. Soils typically contain multiple contrasting layers and often exhibit significantly differing hydraulic conductivity values along preferential flow paths within the soil matrix.
Prior art instruments developed for measuring hydraulic conductivity of soils above the water table in the field have generally fallen into three groups. The first group introduces either a ponded static (i.e., constant) or a variable (i.e., falling) head of water into the bottom of an unlined borehole below the ground surface or into a confining ring in contact with the ground surface. Instruments that establish a static head of water within a borehole maintain the water at a predetermined level, usually by use of either a float and valve system or a marriott tube system. The rate of water flow necessary to maintain a constant water level in the borehole at the predetermined level is utilized to estimate hydraulic conductivity of the soil. Methods used to measure the saturated hydraulic conductivity in a borehole utilizing a constant head of water have been referred to as the shallow well pump-in technique or constant-head well permeameter. Instruments in this first group that utilize a falling head procedure usually measure the drop of water from a predetermined level in a lined or unlined borehole as it dissipates into the soil to estimate hydraulic conductivity.
The second group of instruments applies water through a semi-permeable membrane to a soil surface, which is under negative pressure (tension), to measure unsaturated hydraulic conductivity. The third group of instruments utilizes various methodologies, which include electrical resistivity procedures and gas or liquid injection into the soil through penetrating probes. The instruments in the third group typically require a power source, fluid or gas pumps, multiple chambers, borehole packers, electronic data loggers, and complex analysis procedures.
U.S. Pat. No. 6,105,418 discloses a constant-head float valve assembly which includes a J-shaped fluid conduit for intermittently delivering water from a supply container to a borehole. As the float moves downward with dissipating water levels, a shutoff valve is contacted and thereby opened to replenish the water in the borehole. The rising water moves the float upward and away from the valve, thereby allowing pressure of the incoming water to close the valve again.
U.S. Pat. No. 4,561,290 utilizes a float valve assembly, connected to a water supply reservoir, to regulate water inflow and obtain a constant water level within a borehole. The float responds to a rising water level by regulating water flow through a valve and thereby maintaining a constant water level.
However, neither of these devices incorporates an apparatus for magnifying the vertical force of the float body that is necessary for valve regulation at large depths and flow volumes, nor do they incorporate a backflow check valve to prevent incident entry of suspended soil particles and other contaminates into the float chamber. In addition, neither of these devices includes a means for eliminating the entry of contaminants through its air equalizing passage into the interior of the device.
Soil hydraulic conductivity has been historically measured on a smaller scale in the laboratory, utilizing a falling or constant head of water applied to soil core samples retrieved from the field or on remolded soil samples. Laboratory centrifugal force methods are also utilized to estimate hydraulic conductivity. Laboratory measurements are often significantly at variance with in situ field measurements because of the differing methodologies and the inherent difficulty of obtaining undisturbed soil samples and replicating natural environmental and stress conditions in the laboratory.
It is desirable to have the capability to conduct hydraulic conductivity tests at any depth in earthen materials above the permanent water table. Such depths may range from zero to many meters below the ground surface. In addition, it is desirable to have adequate flow capacity for maintaining flow equilibrium in a wide range of soils. Clay soils often have slow permeability, whereas sandy or gravelly soils often have high permeability and, therefore, a greater equilibrium flow rate.
Prior art inventions that utilize a float system alone do not provide a mechanical advantage ratio, thereby limiting testing to relatively shallow depths. Inventions utilizing the marriott tube principle to establish a constant water level are also limited to relatively shallow depths of testing.
A buoyant force is provided by a float in accordance with Archimedes""s Principle which states that the buoyant force on a body immersed in a fluid is equal to the weight of the fluid displaced by that body. The displacement volume of any float of practical geometric shape that can fit in a small-diameter borehole is relatively small, therefore the depth at which such float can provide throttling of a valve by direct buoyant force alone is limited to relatively shallow depths and small flow rates. There is accordingly a need for an apparatus that is sufficiently rugged and versatile to measure hydraulic conductivities of soils inside a borehole at a variety of depths above the water table, ranging from shallow to deep. There is also a need for a device that can be used inside a borehole, wherein the device is subject to being struck by falling soil particles and debris, without contamination by such particles and debris through the air vent hole at its top or through water outlets at its bottom.
It is an object of the invention to provide a simple and sturdy apparatus which functions as a constant-head soil permeameter for estimating saturated hydraulic conductivity of in situ earthen materials above the water table by establishing a constant head of water at a predetermined level in a borehole that is dug below the ground surface with ordinary hand auger equipment or with power equipment.
It is a further object to provide a soil permeameter that can, without incorporation of electronics, be effectively used to estimate hydraulic conductivity at desired test depths normally encountered above the water table and at depths much greater than the depths at which known devices that utilize a float system can be employed.
It is an additional object to provide a constant-head soil permeameter that can be effectively used to determine hydraulic conductivity within a wide range of soil permeability.
It is also an object to provide a soil permeameter that avoids malfunction in the field by minimizing contamination from soil particles and debris falling from the side of the borehole.
In accordance with these objects and the principles of the invention, the soil permeameter of this invention is an apparatus which incorporates a float and a mechanical linkage system that greatly increases the forces applied by the float to throttle water flow at the control valve.
The constant-head soil permeameter of this invention seeks to overcome disadvantages of other float systems by greatly increasing the buoyant force resulting from submergence of a float alone. The permeameter increases the buoyant force by use of a compound lever and link assembly, as a part of its float system, which provides a mechanical advantage ratio ranging from approximately 10:1 at full valve opening to approximately 60:1 at full valve closure. The resultant available maximum throttling force is, therefore, approximately 60 times greater than simple buoyant force at full valve closure. The effective testing depth range of the permeameter is from 15 centimeters to about 30 meters. The permeability testing range of the apparatus is from 10xe2x88x926 centimeters/second to 10xe2x88x922 centimeters/second. The range of water flow volume through the apparatus is from zero to 2000 milliliters/minute or more at depths greater than one meter.
This constant-head soil permeameter comprises a tubular cylinder having a top end, a bottom end, means for introducing a liquid into the top end, means for selectively closing the bottom end, and means for preventing falling debris and soil from entering the top end while enabling air to flow into and out of the cylinder, the top end and the bottom end being defined in relation to usage within a vertically disposed borehole in materials permeable to the liquid. The cylinder contains a float system that provides a mechanical advantage ratio for shutting off the introduction of liquid.
This float system comprises a compound lever and link assembly that functions as a valve control assembly and is hereinafter thus identified. It is particularly operative when:
A) the liquid is water, the materials are earthen, and the borehole has a bottom disposed above a water table in the earthen materials; and
B) the mechanical advantage ratio ranges from approximately 10:1 at full valve opening to approximately 60:1 at full valve closure.
The valve control assembly, described hereinafter with water as the liquid, comprises the following lever and link assembly:
A) a valve support bracket which is longitudinally disposed and rigidly supported within the cylinder, adjacent to the inner side thereof;
B) an actuating lever arm, having two ends, which is attached at one end to a first pivot which is attached to the valve support bracket;
C) a link, having two ends, which is attached at its lower end to a second pivot which is attached to but spaced apart by a selected distance from the first pivot; and
D) a valve seat retaining lever arm, having two ends, which is pivotally attached at one end to the valve support bracket and is pivotally attached at its other end to a pivot attached to the upper end of the link.
The top end of the cylinder comprises a top stopper, having an upper side and a lower side, which is rigidly attached to the cylinder and is encircled by an o-ring in sealing contact with the cylinder. The means for introducing water into the top end of the cylinder comprises a reservoir for containing water, a hose connection which is rigidly attached to the top stopper and projects outwardly from its upper side and has a bore therewithin, a hose for connecting the reservoir to the hose connection, and a valve body which is rigidly attached to the lower side of the stopper and has a bore therewithin in fluid communication with the bore within the hose connection.
The valve seat retaining lever arm comprises a valve seat which is attached thereto in facing relationship to the valve body and is adapted for selectively shutting off the introducing of water from the reservoir.
The cylinder additionally contains a buoyant float body that is axially movable within the cylinder and has upper and lower surfaces. The upper surface exerts pressure against the other end of the actuating lever arm when the float is supported by water within the cylinder.
The constant-head soil permeameter may be described as comprising the following lever and link assembly which provides a mechanical advantage ratio:
A) a valve support bracket having an upper pair and a lower pair of spaced-apart lugs attached perpendicularly thereto and projecting toward the center of the cylinder;
B) an actuating lever arm having one pair of spaced-apart lugs attached perpendicularly thereto at its pivot end and projecting upwardly, being attached to the lower pair by the first pivot;
C) a link having two pairs of the spaced-apart lugs attached perpendicularly thereto at the upper and lower ends thereof and projecting toward the valve support bracket, one pair being attached by the second pivot to the one pair of spaced-apart lugs on the pivot end of the actuating lever arm and being spaced from the first pivot by a selected distance; and
D) a valve seat retaining lever arm having two pairs of spaced-apart lugs attached perpendicularly thereto at the ends thereof and projecting in opposite directions, one pair being pivotally attached to the upper pair on the valve support bracket and the other pair being pivotally attached to the pair of spaced-apart lugs on the upper end of the link.
The means for preventing falling debris and soil from entering the top end of the cylinder while enabling air to flow into and out of the cylinder comprises an inverted J-shaped tube, having a long portion which passes through the stopper and a short portion having a filter screen at its outer end, the filter screen being disposed to face toward the upper side of the stopper and being spaced from the upper side.
The means for selectively closing the bottom end of the cylinder comprises a bottom stopper, having an upper surface and a lower surface, which is rigidly attached to the cylinder, an o-ring encircling the stopper and in sealing contact with the cylinder, an axially disposed bolt attached to the stopper and extending upwardly beyond its upper surface, at least one longitudinally disposed hole extending through the bottom stopper, and a check valve disposed beneath the lower surface, whereby reverse flow of water from the borehole toward the stopper lifts the check valve and closes the hole and the bottom end.
This constant-head soil permeameter, adapted for operational use within a borehole in earthen materials, comprises a cylindrical housing having a top end and a bottom end which has a flow-through means for allowing water entering the top end to form a first water level within the housing and then to flow through the bottom end into the borehole to form a second water level therewithin when the second water level is lower than the first water level and having a closing means for preventing water from flowing into the cylindrical housing when the second water level is higher than the first water level.
This flow-through means comprises a bottom stopper which is rigidly attached to the cylindrical housing, has a countersunk bottom surface forming a downwardly extending skirt that contacts the bottom of the borehole when the permeameter is resting thereupon, has at least one longitudinally disposed hole through the stopper, and has at least one laterally extending hole through the skirt.
This closing means comprises a check valve guide which is axially and rigidly attached to the countersunk bottom surface of the stopper, a disk-shaped check valve which is loosely and axially fitted to the check valve guide, and a disk-shaped baffle, having a plurality of longitudinally disposed holes therethrough, which is rigidly and perpendicularly attached to the check valve guide and disposed beneath the check valve, whereby backflow of water from the borehole toward the bottom stopper passes through the plurality of holes in the baffle and lifts the check valve to block the at least one longitudinally disposed hole in the bottom stopper.
The rate of water flow into the borehole that is necessary to maintain the constant head is recorded at appropriate intervals during the test period. The information recorded during the test, which also includes height of constant water column, rate of flow, and borehole geometry, is factored into an appropriate mathematical equation to provide an estimate of hydraulic conductivity.